Polyacetal resin composition for fuel-contacting parts

ABSTRACT

A polyacetal resin composition for fuel-related parts having an excellent creeping resistance, high conductivity and high thermal stability in the kneading or molding step is provided. The composition contains (A) a polyacetal resin, (B) glass fibers, (C) a conductive carbon and (D) a polyurethane resin, and has a volume resistivity of not higher than 1×10 5  Ωcm and, as the creeping resistance, such a tensile creep strength that it is not ruptured under a stress of 20 MPa in 60° C. water for at least 200 hours.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a polyacetal resin composition forfuel-related parts comprising a polyacetal resin, glass fibers, aconductive carbon and a polyurethane resin, and having an excellentcreeping resistance, a high conductivity and a high thermal stability inthe kneading or molding step. It is also relates to fuel-related partsproduced therefrom.

2. Background Art

A polyacetal resin is excellent in mechanical properties, fatigueresistance, friction and abrasion resistance, chemical resistance, oilresistance, thermal resistance and moldability. Therefore, it is used ina wide variety of fields such as automobiles, electrical and electronicequipment, other precision machines, and pipes for constructionmaterials. As its use applications become wider, resin compositionshaving improved properties as materials are required and manufactured.As one of those resin compositions, a polyacetal resin containing aconductive carbon black for the purpose of giving conductivity theretois used. For example, the polyacetal resins are used as fuel-relatedparts in consideration of their excellent chemical resistance. But inthis case, since static electricity is generated by shearing of a fueland the resin, the polyacetal resin is required to be conductive.Accordingly, the conductive carbon black is usually blended with thepolyacetal resin.

However, the polyacetal resin has such a serious drawback that the blendof the carbon black noticeably decreases the toughness of the polyacetalresin. And so, when a pipe or the like as the above fuel-related part iscontinuously given a constant pressure or continuously loaded with astress, a creep rupture occurs in a short period of time even if thestress is low.

On the other hand, in order to give the polyacetal resin bothconductivity and a high mechanical strength, a surface-treated carbonfiber is added thereto. Such a polyacetal resin, however, cannot be usedas general-purpose materials due to a highly increasing cost.

Therefore, there has been desired a polyacetal resin composition forfuel-related parts which can be manufactured at a low cost and which hasa high conductivity, a high toughness, and in particular, an excellentcreep resistance.

DISCLOSURE OF THE INVENTION

The present inventor has intensively investigated to obtain a polyacetalresin composition for fuel-related parts having excellent properties asdescribed above. As a result, he has found that it is extremelyeffective to blend glass fibers, a conductive carbon and a polyurethaneresin with a polyacetal resin and, in consequence, the present inventionhas been completed.

That is, the present invention relates to a polyacetal resin compositionfor fuel-related parts which is obtained by blending (A) a polyacetalresin with (B) glass fibers, (C) a conductive carbon and (D) apolyurethane resin, and which has a volume resistivity of 1×10⁵ Ωcm orless and, as a creep resistance, such a tensile creep strength that itis not ruptured under a stress of 20 MPa in 60° C. water for at least200 hours.

In a word, the present invention relates to the composition containingthe above-described (A), (B), (C) and (D) and having the volumeresistivity and the tensile creep strength as described above, and thefuel-related parts produced therefrom.

DETAILED DESCRIPTION OF THE INVENTION

The constitutional components of the present invention will be describedhereinafter.

The polyacetal resin (A) according to the present invention is a polymerhaving oxymethylene groups (—CH₂O—) as the main repeating unit, and sucha polyacetal resin includes polyoxymethylene homopolymers and polyacetalcopolymers. The copolymers contain, other than the oxymethylene groups,oxyalkylene groups having about 2 to 6 carbon atoms, preferably about 2to 4 carbon atoms (e.g., an oxyethylene group (—CH₂CH₂O—), anoxypropylene group, an oxytetramethylene group or the like). The contentratio of the oxyalkylene units having about 2 to 6 carbon atoms can besuitably selected in accordance with the application of the polyacetal,for example, 0.1 to 30 mol %, preferably 1 to 20 mol % based on thetotal polyacetal.

The polyacetal copolymer can be constituted of a plurality of componentssuch as a copolymer consisting of two components and a terpolymerconsisting of three components, and it may be a block copolymer. Thepolyacetal resin may be not only a linear one but one having a branchedor cross-linked structure. Further, the terminals of the polyacetalresin may be stabilized by esterification with carboxylic acids such asacetic acid, propionic acid and butyric acid. The degrees ofpolymerization, branching and cross-linking of the polyacetal resin arenot particularly restricted so long as the resin is meltable andmoldable.

Preferable polyacetal resins include polyoxymethylene homopolymers andpolyacetal copolymers (e.g., a copolymer comprising at least both anoxymethylene unit and an oxyethylene unit). Preference is given to thepolyacetal copolymers from the standpoint of thermal stability.

A molecular weight of the aforesaid polyacetal resin is preferably aslarge as possible. The larger the molecular weight is, the more thecreep resistance improves. Concretely, it is preferred that a melt indexat 190° C. of the resin is not more than 9.0 g/10 min.

The aforesaid polyacetal resin can be produced by a conventional method,for example, by polymerizing aldehydes such as formaldehyde,paraformaldehyde and acetaldehyde, and cyclic ethers such as trioxane,ethylene oxide, propylene oxide and 1,3-dioxolane.

The glass fibers (B) usable in the present invention are not particularrestricted. In view of handling, a chopped strand being cut intoapproximately 2 to 8 mm lengths is preferable. The glass fiber having adiameter of usually 5 to 15 μm, preferably 7 to 13 μm can be suitablyused.

As the glass fiber, it is also preferred to use a surface pre-treatedone. As a material for the surface treatment, polyurethane resins oroligomers are preferred. Such surface treated glass fibers can be easilyhandled.

The conductive carbon (C) used in the present invention is notrestricted to particular ones. Any of Ketchen Black, acetylene black,channel black or various furnace type conductive carbons having anaverage particle size of 1-500 mμ, preferably 10-100 mμ can be used.

The polyurethane resin (D) used in the present invention is a polymer oran oligomer having an urethane linkage in the main chain. Generally, inmany cases, a reactive functional group such as a hydroxyl group ispresent at the end of the polymer chain or a functional group includinga hydroxyl group is suspending from the main chain. The polyurethaneresin includes, for example, thermoplastic polyurethanes prepared byreacting a polyisocyanate component such as aliphatic, alicyclic oraromatic polyisocyanates with a polyol component such as a lowermolecular weight polyol component, e.g., aliphatic, alicyclic oraromatic polyols, polyether diols, polyester diols and polycarbonatediols. In the preparation of the polyurethane, use may be made of achain elongating agent such as diols or diamines. Furthermore,polyurethane elastomers may also be included in the polyurethane resin.These polyurethane resins may be used alone or in combination of two ormore of them.

In the present invention, an addition of such a polyurethane resinresults in the improvement of melt stability and processability of theconductive polyacetal resin. That depresses the decomposition during themolding or processing and enhances mechanical strength and creepresistance.

The polyurethane resin may be not only linear but also blanched orcross-linked as long as it can maintain thermoplasticity. Among thesepolyurethane resins, preference is given to the polyurethane and thepolyurethane elastomer which are produced by reacting a diisocyanatecomponent with a diol component.

A molecular weight of the polyurethane resin is not restricted. Forexample, from oligomers having a molecular weight of at most 10,000 topolymers having a molecular weight of at least 100,000 can be uesd.

Examples of the diisocyanate component are aliphatic diisocyanates suchas 1,6-hexamethylene diisocyanate, alicyclic diisocyanates such asisophorone diisocyanate, aromatic diisocyanates such as 2,4-toluenediisocyanate, 2,6-toluene diisocyanate and 4,4′-diphenylmethanediisocyanate, and others.

Examples of the diol component are C₂-C₁₀alkylene diols, polyoxyalkyleneglycols such as poly(oxyethylene)glycol, poly(oxypropylene)glycol,poly(oxytetramethylene)glycol or copolymer glycols thereof such aspolyethylene oxide-polypropylene oxide block copolymer, etc., polyesterdiols such as a polyesterdiol which is produced by the condensationpolymerization of C₄-C₁₂ aliphatic dicarboxylic acids, e.g.,polyethylene adipate or polybutylene adipate containing terminalhydroxyl groups, with C₂-C₁₆ aliphatic diols, and others.

A polyurethane elastomer is more useful than a polyurethane resin forimproving melt stability and processability of the conductive polyacetalresin. The polyurethane elastomer includes, for example, a polyurethaneelastomer which is produced by reacting the aforesaid diisocyanatecomponent with a diol component such as polyoxyalkylene glycols andpolyester diols containing polyoxyalkylene glycol units.

These polyurethane resins may be previously added as a surface-treatingagent for glass fibers (B).

It is important that the polyacetal resin composition for fuel-relatedparts of the present invention is prepared so as to have a volumeresistivity of not higher than 1×10⁵ Ωcm and, as the creep resistance,such a tensile creep strength that the resin composition is not rupturedunder a stress of 20 MPa in water at 60° C. for at least 200 hours bycomprising a polyacetal resin (A), glass fibers (B), a conductive carbon(C) and a polyurethane resin (D) described above.

As a preparation method of the aforesaid resin composition, there may bementioned a method of blending 100 parts by weight of the polyacetalresin (A) with 5 to 20 parts by weight of the glass fibers (B), 5 to 20parts by weight of the conductive carbon (C), and 0.01 to 10 part(s) byweight of the polyurethane resin (D) one another.

An amount of the glass fibers (B) to be added is preferably 5 to 20parts by weight, more preferably 8 to 15 parts by weight. Within such anamount range, the creep resistance may be improved and the flowabilityand extrusion processability may become good.

An amount of the conductive carbon (C) to be added is preferably 5 to 20parts by weight, more preferably 7 to 12 parts by weight. Within such anamount range, sufficient conductivity as well as good toughness and heatstability of the polyacetal resin may be obtained.

An amount of the polyurethane resin (D) to be added, which includes theamount of the polyurethane resin to be added as a surface treating agentfor the glass fibers (B), is preferably 0.01 to 10 part(s) by weight,more preferably 0.01 to 3 part(s) by weight. Within such an amountrange, melt stability and extrusion/molding processability of theconductive polyacetal resin are improved, and the foaming during theextrusion and formalin odor are not generated. The present resincomposition can be used widely as fuel-related parts with its goodmechanical strength and creep resistance.

Further, a stabilizing agent for improving heat stability is preferablyadded to the present resin composition.

Optionally, one or more of the usual additives such as UV absorbents,lubricants, mold releasing agents, colorants including dyes and pigmentsand surface active agents can be added, if necessary.

The composition of the present invention may be easily prepared by theknown conventional methods generally used as a method for thepreparation of the resin composition. For example, a method wherein thecomponents are mixed with each other and then kneaded and extruded in anextruder to prepare pellets; a method wherein pellets having differentcompositions are prepared, and then they are mixed with each other in apredetermined ratio and subjected to molding to obtain a molded producthaving a desired composition; a method wherein one or two or more of thecomponents are directly charged in a molding machine. Any of thesemethods may be used.

The polyacetal resin composition for fuel-related parts of the presentinvention is applied with conductivity and high creep resistance besidesthe chemical resistance, which a polyacetal resin originally has, sothat it can be widely used for various fuel-related parts, and it isalso improved on melt stability and extrusion/molding processability bythe addition of a polyurethane resin.

EXAMPLES

The present invention will be further elucidated on the basis of thefollowing Examples and Comparative Examples, but the scope of thepresent invention shall not be limited to these Examples.

Examples 1 to 7 and Comparative Examples 1 to 5

A polyacetal resin (A), glass fibers (B), a conductive carbon (C) and apolyurethane resin (D), whose types and amounts are indicated in Tables1 and 2, were mixed with each other and melt kneaded in a 30 mmtwin-screw extruder at 190° C. to prepare pellets which were thenevaluated.

The conductivity, creep resistance and mechanical properties of themolded articles were evaluated as follows:

Volume Resistivity

A disk-like test piece having a diameter of 100 mm and a thickness of 3mm was used. Conductive paste was applied on both side of the disk, anddried. Then, volume resistivity was calculated by measuring electricresistance of the sample.

Creep Resistance

An ASTM D-638 test piece was used. A constant stress, 20 MPa, wasapplied on the sample in water at 60° C. The time needed to rupture thesample was determined.

Tensile Property

The determination was carried out according to ASTM D-638.

Moldability

Evaluation was carried out by the observation of foaming and formalinodor during the compounding in the following three levels.

⊚: Neither foaming nor formalin odor

◯: No foaming but a little formalin odor

X: Foaming and heavy formalin odor

The following glass fibers, conductive carbons and polyurethane resinswere used in the Examples and Comparative Examples:

(B) Glass Fiber

(1) “Chopped Strand 3J-948”; trade name, manufactured by Nitto-BosekiCompany (epoxy-treated glass fibers)

(2) “Glossrun Chopped Strand CS 03 JA FT102”; trade name, manufacturedby Asahi Fiberglass Company (urethane-treated glass fibers)

(C) Conductive Carbon

“Ketchen Black ECX”; trade name, manufactured by Ketchen BlackInternational Company

(D) Polyurethane Resin

Thermoplastic polyurethane (“Miractoran E375MSJP-1”; trade name,manufactured by Nippon Miractoran Co., Ltd.)

TABLE 1 Example Example Example Example Example Example Example 1 2 3 45 6 7 Amount (A) Polyacetal Resin 100 100 100 100 100 100 100 (pts. wt.)(B) Glass Fiber (1) 8 12 15 12 — — — (B) Glass Fiber (2) — — — — 12 1512 (C) Conductive carbon 8 8 8 12 8 8 8 (D) Polyurethane Resin 1 2 3 2 —— 2 (D) Polyurethane Resin used as — — — — (0.12) (0.15) (0.12) SurfaceTreatment Agent for (B) Physical Volume Resistivity (Ω · cm) 1.6 × 10⁴9.5 × 10² 2.2 × 10² 1.4 × 10² 8.1 × 10² 2.0 × 10² 8.3 × 10² PropertiesCreep resistance time (hr) 250 300 350 250 300 330 310 Tensile Strength(MPa) 67.7 72.5 75.9 71.4 75.1 78.2 77.3 Tensile Elongation (%) 3.5 3.12.8 3.0 3.2 3.0 3.1 Moldability ⊚ ⊚ ∘ ∘ ∘ ∘ ⊚

TABLE 2 Comparative Comparative Comparative Comparative ComparativeExample Example Example Example Example 1 2 3 4 5 Amount (A) PolyacetalResin 100 100 100 100 100 (pts. wt.) (B) Glass Fiber (1) 8 — 8 12 — (B)Glass Fiber (2) — — — — 8 (C) Conductive carbon — 8 8 8 — (D)Polyurethane Resin 1 1 — — 1 (D) Polyurethane Resin used as — — — —(0.08) Surface Treatment Agent for (B) Physical Volume Resistivity (Ω ·cm) >10¹² 7.4 × 10⁵ 3.4 × 10⁴ 2.6 × 10³ >10¹² Properties Creepresistance time (hr) 270 80 120 150 270 Tensile Strength (MPa) 70.0 58.162.2 64.1 72.1 Tensile Elongation (%) 3.7 5.5 2.9 2.6 3.8 Moldability ⊚⊚ x x ⊚

What is claimed is:
 1. A polyacetal resin composition for fuel-relatedparts comprising: (A) 100 parts by weight of a polyacetal resin, (B) 5to 20 parts by weight of glass fibers, (C) 5 to 20 parts by weight ofconductive carbon, and (D) 0.01 to 10 parts by weight of a polyurethaneresin, wherein said composition exhibits a volume resistivity of nothigher than 1×10⁵ Ωcm and a creep resistance such that a test pieceaccording to ASTM D-638 formed of the composition does not rupture undera stress of 20 MPa in 60° C. water for at last 200 hours.
 2. Thecomposition according to claim 1, wherein the glass fibers arepretreated with the polyurethane resin and have a diameter of 7 to 13mm.
 3. The composition according to claim 1, wherein the polyacetalresin has a melt index at 190° C. of not more than 9.0 g/10 min. 4.Fuel-related parts comprising the composition according to claim 1.